The present invention relates generally to perspective transformation processes employed in radar system signal processors, and more particularly, to a process for enhancing the quality of an image following a perspective transformation from image data in the range-azimuth coordinate system (B-scan) into image data in the elevation-azimuth coordinate system (C-scan).
A product known as a TMC 2301 image resampling sequencer manufactured by TRW LSI Products performs image manipulation in video, graphics, medical, radar, and other image processing systems. It uses a 2nd order Taylor series to perform coordinate transformations from Cartesian (x,y) format to C-scan format. Together with another product known as a TMC 2330 coordinate transformer available from the same company, which transforms from B-scan format to Cartesian format, an approximation to the transformation from B-scan to C-scan formats can be achieved.
Typically the perspective transformation performed by the above-described equipment is not a one-to-one mapping of a point in C-scan with a point in B-scan. For a transformation process that computes a range-azimuth point for a given elevation-azimuth point, there may be many range cells covered by adjacent elevation points in farther range cases, or there may be a single range cell covering many elevation points in nearer range cases. Without image enhancement, such as is performed by the present invention, the transformed image will have missing data points at the far range, and large areas that have the same data point at the near range.
A conventional way to handle the missing data point problem in the far range cases is to average all the range data that is within range cells given by the two adjacent elevation points. However, this will artificially smooth the image contrast at the far range. Normally bright objects such as aircraft, airport lights, trucks, or hangers at the far range will be averaged with the background and will not be seen. Normally dark objects such as runways and taxiways at the far range will also be averaged with the background and will be lost.
In a copending U.S. patent application Ser. No. 08/269,407, filed Jun. 30, 1994, entitled "Precision High Speed Perspective Transformation From Range-Azimuth Format to Elevation-Azimuth Format", assigned to the assignee of the present invention, an improved process for making the above-described B-scan to C-scan transformation is described. The present invention is directed toward improving the quality of the transformed image subsequent to transformation by this and other conventional B-scan to C-scan converters.
In view of the above, it is an objective of the present invention to provide for an image data enhancement process that enhances the image quality of transformed B-scan to C-scan images provided by the perspective transformation processor described in the above-cited patent application and other conventional B-scan to C-scan converters.